J. Anat. (1980), 131, 3, pp. 525-540 525 With 1Ofigures Printed in Great Britain A reappraisal of the anatomy of the human lumbar erector spinae NIKOLAI BOGDUK Division ofNeurology, Prince Henry Hosptial and Department ofMedicine, University ofNew South Wales, Sydney, Australia (Accepted 2 April 1980) INTRODUCTION In the course of a study of the lumbar dorsal rami, observations were made of the gross anatomy of the lumbar erector spinae muscle. It was found that the observa- tions made were at variance with the descriptions of this muscle given in textbooks. The variance was so marked that it was considered appropriate formally to present the observations and their ramifications, and to reappraise the current interpretation of the anatomy of the lumbar erector spinae. METHODS The lumbar erector spinae was studied by gross dissection in four embalmed adult cadavers. The detailed anatomy of the muscle was studied by systematically resecting its component fascicles and noting their disposition and attachments. The more superficial and lateral fibres were resected first. This revealed the more deeply lying fibres which were then dissected in turn, until the entire erector spinae had been resected. The study was restricted to the fleshy longissimus thoracis and iliocostalis lumborum components of the erector spinae. The spinalis thoracis (dorsi) is mainly aponeurotic in the lumbar region and was not included in the study. The spinalis thoracis and its variations have been fully described previously (Winckler, 1937). RESULTS The lumbar erector spinae is a large muscle mass lying lateral to the multifidus muscle (Fig. 1). It is largely covered by an aponeurosis, the erector spinae apo- neurosis, which arises from the dorsal segment of the iliac crest, the sacral and lumbar spinous processes and the intervening supraspinous ligaments. The tendinous fibres of the aponeurosis pass rostrolaterally across the multifidus and erector spinae until they become fleshy. The aponeurosis also gives rise to other fleshy fibres of the lumbar erector spinae from its deep and superficial surfaces (q.v.). On inspection (Fig. 1), the lumbar erector spinae in the dorsal lumbar region appears to be a common muscle mass which, as it enters the dorsal thoracic region splits into medial and lateral divisions which are separated by the iliocostalis thoracis. Dissection of the common muscle mass, however, reveals that the segrega- tion into medial and lateral divisions is also manifest in the lumbar region. The common mass of the lumbar erector spinae is divided into two divisions by the 0021-8782/80/2828-8260 $02.00 © 1980 Anat. Soc. G.B. & I 526 N. BOGDUK .tus .~~~~~~~~~~~~~~~~~~~~ _~~~~~~~~~~~~~ t S " . A l neurosis~~(a)Ontelf,telmaercospaeshasbersctdodmntaeth2 relative positions of the iliocostalis thoracis (it) and multifidus (in). The posterior superior iliac spines (ps) and lumbar transverse process (tp) are marked. (B) The lateral division (id) of the lumbar erector spinae (iliocostalis lumborum) has been reflected to demonstrate the cleavage planes about iliocostalis thoracis (it) which separate the lateral division from the medial division (md) (longissimus thoracis). The lumbar erector spinae 527 erector spinae aponeurosis and an intermuscular aponeurosis. This latter aponeurosis has no formal name (Nomina Anatomica, 1977), so it is referred to herein as the lumbar intermuscular aponeurosis. The lumbar intermuscular aponeurosis The lumbar intermuscular aponeurosis stems from the ilium. It is attached to a linear area on the medial aspect of the dorsal segment of the iliac crest just rostral to the posterior superior iliac spine. This line of attachment extends some 2-3 cm ventrolaterally across the medial aspect of the iliac crest (Fig. 2). From this origin 528 N. BOGDUK PS Fig. 2. An illustration of the rostromedial aspect of the right ilium showing the areas of attach- ment of the erector spinae aponeurosis (esa), the lumbar intermuscular aponeurosis (lia), the lumbar fibres of the lateral division (Id) and medial division (md), of the erector spinae and the multifidus (mf). For orientation, the fifth lumbar vertebra (L5) and the iliolumbar ligament (ill) and posterior superior iliac spine (ps) are marked. Note the area (f) where the fat ventral to the lumbar intermuscular aponeurosis contacts the ilium. r lia t L k" '; kR = e _ >;! l, x v *~~~~~~~~~~~4, e Fig. 3. A dorsal view of a dissection of a left lumbar intermuscular aponeurosis (lia). The dorsal lumbar muscles have all been resected leaving an isolated intact intermuscular aponeurosis. The posterior superior iliac spines (ps) have been marked. On the right note how little of the erector spinae aponeurosis (esa) extends lateral to the plane of the lumbar intermuscular aponeurosis (arrow). The lumbar erector spinae 529 Fig. 4. A dorsolateral view of a left lumbar intermuscular aponeurosis (lia) showing its extent into the dorsal lumbar region. The Ll-L2 zygapophysial joint is marked (zj). the tendinous fibres of the aponeurosis fan out into the lower half or so of the dorsal 41 lumbar region (Figs. 3, 4). The plane of the aponeurosis is essentially parasagittal, but rotated somewhat laterally so that it presents rostral, ventral and dorsal edges, and ventromedial and dorsolateral surfaces. The rostral and ventral edges of the lumbar intermuscular aponeurosis are irregular because its tendinous fibres become fleshy muscle fibres. The ventral edge reaches almost to the dorsal surfaces of the lumbar transverse processes, but is separated from them by a fat-filled space (Figs. 5, 6). The fat contacts the dorsal surfaces of the L1-L4 transverse processes at about their middle third. Over this contact area the transverse processes are free of muscle attachments (Figs. 6, 7). Caudally, the fat contacts the ilium ventral to the ventral end of the attachment of the lumbar intermuscular aponeurosis (Fig. 2). The lateral branches of the upper lumbar dorsal rami course through this fat-filled space and, within it, divide into their branches (Fig. SB). Along its dorsal edge the lumbar intermuscular aponeurosis is continuous with the erector spinae aponeurosis (Fig. 5B) and it appears to be actually a ventral reflection of the erector spinae aponeurosis (Fig. 6). Indeed, because little of the erector spinae aponeurosis extends lateral to the plane of the lumbar intermuscular aponeurosis (Fig. 3) the latter would appear to be the principal continuation of the erector spinae aponeurosis, diving ventrally into the lumbar erector spinae. The ventromedial and dorsolateral surfaces of the lumbar intermuscular aponeurosis give rise to fleshy fibres of the lumbar erector spinae. 530 N. BOGDUK AL-- -t The lumbar erector spinae 531 Fig. 6. A diagramatic transverse section of the lower lumbar region showing the relative dis- position of the muscles, fasciae and aponeuroses. The erector spinae aponeurosis (esa) covers the interspinalis (I), multifidus (MF), and the medial division (MD) of the lumbar erector spinae, viz. longissimus thoracis (LT). It is continuous ventrally with the lumbar intermuscular apo- neurosis (lia) which envelopes the lateral surface of the medial division, segregating it from the lateral division (LD), viz. iliocostalis lumborum (IL). The fat-filled space (fs) ventral to the lumbar intermuscular aponeurosis maintains this segregation as far as the transverse process. The medial division inserts about the accessory process (ap) while the lateral division inserts further laterally on the transverse process. Lateral to the lumbar intermuscular aponeurosis the erector spinae aponeurosis extends for a limited distance over the dorsal surface of the lateral division (cf. Fig. 1). The intertransversarii mediales (IM) are marked. The lumbar intermuscular aponeurosis and erector spinae aponeurosis form a continuous aponeurotic envelope which, in the lumbar region, divides the lumbar erector spinae into a medial and a lateral division (Fig. 6). Medial division of the lumbar erector spinae In the lumbar region the medial division of the lumbar erector spinae lies medial to the lumbar intermuscular aponeurosis and deep to the erector spinae aponeurosis (Fig. 6), while in the thoracic region it lies medial to iliocostalis thoracis (Fig. 1). Within the medial division lumbar and thoracic fibres may be identified. The lumbar fibres are those which insert into lumbar vertebrae. The thoracic fibres insert into thoracic vertebrae and ribs. The lumbar fibres of the medial division of the lumbar erector spinae arise from the medial aspect of the middle third or so of the dorsal segment of the iliac crest and from the medial surface of the lumbar intermuscular aponeurosis (Fig. 8). The attachment to the lumbar intermuscular aponeurosis is strong and dense. The muscle fibres are arranged in five laminae, each directed to a certain lumbar vertebra (Figs. 8, 9). The more caudal fibres from the ilium form the deepest laminae. They pass Fig. 5. (A) A lateral view of the right lumbar erector spinae and erector spinae aponeurosis (esa) with an outline of the area dissected and shown in close up in Fig. 5(B). For orientation, the posterior superior iliac spine (ps) and the lateral branches of the L3 and Li dorsal rami (L3 dr, Li dr), where they cross the iliac crest, have been marked. The lateral division (Id) ofthe lumbar erector spinae (iliocostalis lumborum) was resected to produce Fig. 5 (B). (B) A close up lateral view of a right lumbar intermuscular aponeurosis (lia). Note its continuity with the erector spinae aponeurosis (esa) dorsally; its irregular ventral edge (e), and the fat-filled space (fs) ventral to it through which lateral branches (lb) of the lumbar dorsal rami course. 532 N. BOGDUK Fig. 7. An illustration of the insertions of the lumbar fibres of the medial division (md) and the lateral division (Id) of the lumbar erector spinae. Note the areas (f) on the transverse processes free of muscle attachment which are in contact with the fat ventral to the lumbar intermuscular aponeurosis, and the tendinous (t) insertion into the tips of the accessory processes and the more fleshy insertion about their bases, of the medial division.